In the commercial meetings or conferences of companies or schools, it is often needed to indicate some literal or graphical data during discussions or briefings. A document camera is thus popularly used to facilitate the presentation or discussion of a document, chart or academic thesis. Such a document camera is so-called a teaching material prompting machine, or, most commonly, an object-image projector.
A common object-image projector combines the functions of photographing, scanning, and image output of cameras or scanners. The photo module can be, for example, a digital video recorder, a digital statistic camera, a cell phone with a camera module, a monitor camera, or a PC camera. According to current technology, there are several available types of camera modules which are different in manufacturing processes, prices, sensitivities of pixels, sums of power consumption, etc. These camera modules can be classified as two main types, i.e. camera modules equipped with complementary metal-oxide semiconductor (CMOS) sensors and equipped with charged coupled device (CCD) sensors. The sensors act as the film of a conventional camera. A conventional camera film performs the development according to the change of the film resulted by a chemical reaction occurred according to light sensed by the film. On the other hand, image sensors such as the CMOS or CCD sensors, by utilizing the photo-electric converting effect, generate electric charges with a number variant with the intensity of sensed light, and thus form the current to be outputted.
However, according to different requirements, CMOS/CCD image sensors can be applied in different fields. Generally speaking, when compared with the CMOS image sensors, the CCD image sensors have maturer manufacturing technique and higher pixel number or dpi. Therefore, the CCD image sensors are often applied in digital statistic cameras or digital video recorder having middle/high level dpi. However, the CCD image sensors have defects of high power consumptions and prices. Furthermore, most manufacturing processes are stilled monopolized by Japanese manufacturers. On the other hand, although the CMOS image sensors have smaller dpi values than those of the CCD image sensors, the CMOS image sensors are benefited in capable of being manufactured in standard semiconductor manufacturing processes. Therefore, the CMOS image sensors can be manufactured in mass production. Furthermore, the CMOS image sensors are also benefited in their low power-consumptions and low prices. Therefore, the CMOS image sensors are wildly applied in the camera modules of cell phones and PC cameras, which do not need high dpi values. Consequently, the CMOS/CCD image sensors can be optionally selected to be the main structure of the camera module of an object-image projector according to the requirement of application. Except for capturing an image of a 3D object, the object-image projector can also be applied with image devices such as an image scanner or a fax machine which are capable of scanning documents or pictures to be projected to a project screen via a common triple-beam/single-beam digital projector, or outputted to a monitor of a common television or computer system to undergo a live video of the image of the object to be projected.
Therefore, according to such an operation of the object-image projector, the users can directly present lecture notes, references, drawings or the like to the audiences on the monitor of a computer or a projecting screen without previously scanning or color/black-and-white copying these projecting object to the transparent projection slices. Hence, the object-image projector has not only reduced the loading of preparing the presentation materials, but also provided a greater convenience and flexibility for the users during the presentations.
Referring to FIG. 1(a), there is a conventional object-image projector 10 which indicates an image of a presenting object 1 on the project screen 21. The image of the presenting object 1 is obtained by capturing or scanning of the image-capturing module 11 (constructed mainly by the CCD or CMOS sensor) of the object-image projector 10 and then projected by a single-beam digital projector 20 to the project screen 21. In other words, a real-time video image of the presenting object 1 will be indicated on the project screen 21 once the presenting object 1 is placed in front of the image-capturing module 11. Preferably, there is a zoom lens on the image-capturing module 11 so as to zoom in or zoom out a certain portion of the presenting object 1 for facilitating the observation.
FIG. 1(b) illustrates a block diagram of the operation of the conventional object-image projector 10. The inside of the conventional object-image projector 10 includes a digital signal processor (DSP) 12, an image synthesis device 13, a memory 14, and a digital/analog converter 15. The image-capturing module 11 also includes an analog/digital converter 111 for converting the analog image signal into a digital format signal to be transferred to the DSP 12 to be processed. For example, the signal is processed after an image zoom-in or zoom-out, and the processed signal can be transferred to the image synthesis device 13 to be synthesized with other image. Furthermore, different images can be stacked up. Moreover, the image of the presenting object 1 captured or scanned by the image-capturing module 11 can be stored in the memory 14 in a picture or image file format after being processed by the DSP 12.
In other words, the image of the presenting object 1 can not only be real-time displayed, but also be synthesized with the other image stored in the memory 14. The image stored in the memory 14 can be an image of another presenting object previously captured by the image-capturing module 11. The synthesis of the real-time image and the previously stored image enables the user to display and compare the present/previous presenting objects. The synthesized image signal processed by the image synthesis device 13 is a digital signal and can be converted into an analog signal by the digital/analog signal converter 15 to be projected by the single-beam digital projector 20 to the project screen 21.
However, according to the current prior art, the synthesis image frame of the real-time image of the presenting object 1 and the previous image stored in the memory 14 is often processed by the electronic panning, i.e., the synthesis image frame are evenly divided into two portions for displaying both images. An example of the synthesis image frame is shown in FIGS. 1(c) and 1(d), the conventional object-image projector 10 indicates two image frames simultaneously on the project screen 21. As shown in FIG. 1(c), the synthesis image frame is constructed by an object image frame P1 indicated by an image captured from the presenting object 1, and a file image frame P2 indicated by an image read from a record file stored in the memory 14. In an example case, the object image frame P1, the file image frame P2, and the display range of the project screen 21 all have 800×600 pixels, and the initial coordinates are all (1, 1) as well. The left portion of the object image frame P1, i.e. pixels from (1, 1) to (400, 600) in P1, is indicated on the left portion of the project screen 21. Meanwhile, what is indicated on the right portion of the project screen 21 is the right portion of the file image frame P2, and the display range is from pixel (401, 1) to pixel (800, 600) of the file image frame P2.
It is observed that only a half of the object image frame P1 and only a half of the file image frame P2 can be indicated on the project screen 21. However, if it is desired to change the view scope of the object image frame P1 or the file image frame P2 on the project screen 21, e.g. change the view scope to the object image frame P1 to the right portion or change the view scope of the file image frame P2 to the left portion so as to facilitate the observation or comparison of the two images, the only way in the conventional method is to apply the electronic panning on the image of the image frame P1 or P2 so as to shift the view scope of the image in the image frame to a desired range just as to scroll an image in a window. Such an operation can be performed via an operation interface of the object-image projector, e.g. a remote controller. According to the electronic panning, the user can, as shown in FIG. 1(d), indicate the right portion (from (401, 1) to (800, 600) of the object image frame P1 on the project screen 21, and the left portion (from (1, 1) to (400, 600)) of the file image frame P2. However, such an electronic panning can only change the view scope range other than the view scope size. In other words, the image in either the object image frame P1 or the file image frame P2 can only be observed in a scope size, in the maximum case, a half of the project screen 21. Such a limitation disadvantages the observation or comparison of the two images in both image frames. It is then attempted by the invention to solve the problems.